Bearing devices which make use of balls or rollers arranged between outer and inner races are widely used for the smooth running of rotary components in equipment of the most diverse sizes from heavy industrial equipment to electronic devices. Traditionally, such bearing balls and rollers have been manufactured from steel but, in recent years, ceramic materials, such as, for example, silicon nitride also have been used.
Steel and super-steel have heretofore been the material of choice for bearing balls in, for example, hard disk drives for computers. However, with improvements in computer performance, higher rotational frequencies have been demanded, and, accordingly, it has become necessary to make use of ceramic materials (ball manufacturing material) for the manufacture of bearing balls. One type of hard disk drive of the nature incorporating ceramic bearing balls is described and illustrated in U.S. Pat. No. 5,485,331 to Dunfield et al., issued Jan. 16, 1996.
Since the density of ceramic materials is generally lower than that of steel, the weight and hence the frictional resistance of ceramic bearing balls is correspondingly lower. Also, since the thermal expansion coefficient of ceramic materials is lower than that of steel, the dimensional accuracy can be improved. A ceramic material also has the advantage of requiring less lubricant.
However, merely selecting a ceramic material for a bearing ball is not necessarily sufficient in itself. For example, in a computer hard disk drive, irregular bearing vibrations during the storage (writing) and reading of data constitutes a potentially fatal performance drawback. Balls for such a bearing therefore demand a greater performance accuracy than that of the bearing balls used in a machine tool, for example.
It is therefore an object of the present invention to provide a ceramic bearing ball which is capable of preventing irregular vibration of, for example, a hard disk drive incorporating the ceramic bearing ball.